Need Component Selection For RPS  - Page 1
Forum section: electronics / beginners

author: ommsiva
author_rank: Regular Contributor
timestamp: December 29, 2023, 04:37:19 am
content: Hi,I am third year Student who want build power supply(0-30V, 0-5A CC CV). I went through the circuit which i have attached, but the components are obsolete. Kindly Help me in getting Alternate Components or Complete Circuit. Thank you all.

author: ommsiva
author_rank: Regular Contributor
timestamp: December 29, 2023, 01:00:39 pm
content: I went through net and got this circuit. I don't know what will happen when a short circuit is made at the output. Kindly request to give feedback about the LM723 circuit.

author: Andy Chee
author_rank: Super Contributor
timestamp: December 29, 2023, 01:10:27 pm
content: Quote from: ommsiva on December 29, 2023, 01:00:39 pmUnder short circuit conditions, the high current creates a large voltage drop across R5. This large voltage causes the LM723 to reduce output voltage until the current through R5 falls back below the current limit setting (adjustable using P1).

author: ommsiva
author_rank: Regular Contributor
timestamp: December 29, 2023, 01:24:14 pm
content: under what conditions the series pass transistor will go to breakdown condition?

author: Andy Chee
author_rank: Super Contributor
timestamp: December 29, 2023, 01:39:31 pm
content: Quote from: ommsiva on December 29, 2023, 01:24:14 pmThe series pass transistor Q2 is a 2N3055. Here is the datasheet:https://www.onsemi.com/pdf/datasheet/2n3055-d.pdfFigure 2 on page 2 contains the safe operating area graph. Operating the pass transistor outside this region will cause breakdown.

author: ommsiva
author_rank: Regular Contributor
timestamp: December 29, 2023, 02:23:25 pm
content: Thank you sir.My doubt is , when the load is 3V@3amps, power=9 watts. Then remaining 27V*3A=81Watt has to dissipate in series pass element. How much time the circuit can give regulated output avoiding breakdown. What is the heat sink to be used?

author: Andy Chee
author_rank: Super Contributor
timestamp: December 29, 2023, 03:02:55 pm
content: Your analysis is correct, 81 watts is a lot of heat.If you examine Figure 2 on the datasheet, your operating condition 27V @ 3A is very close to the limit. For safety and reliability margin, I would use 3 x 2N3055 instead of 1 x 2N3055. This means the operating condition is 27V @ 1A per transistor. You will require some circuit changes to use parallel pass transistors.Total power is still 81 watts (27 watts per transistor), so you need a VERY big heatsink with fan. See the following website for more info on calculation:https://sound-au.com/heatsinks.htmI estimate heatsink resistance 0.1degC/W maximum, but this will depend on the operating environment (indoors air conditioned 25degC, or outdoors in direct sunlight 45degC).

author: ommsiva
author_rank: Regular Contributor
timestamp: December 29, 2023, 04:48:41 pm
content: I want to know in what way the circuit can go wrong??? Is it not liable to failure???

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 05:15:36 am
content: Quote from: ommsiva on December 29, 2023, 04:48:41 pmOverheating the pass transistor is one failure point. Also there may be feedback oscillation instability.If these failures cause the pass transistor to short circuit, the input unregulated voltage will be directly connected to the output, potentially causing damage to whatever was connected to the output.

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 05:51:33 am
content: Sir,Here is a circuit where opamp is present as feedback element. I cant understand how current limiting is done.1)Why there is LED ,diode at the output of opamp.2)Kindly explain P2,R3,R4,P1,D2,C5,C7,R2,R5.3)why there is -1.2 volt between R9 and P4 from output of 7905 regulator?Thank you all

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 06:16:03 am
content: Quote from: ommsiva on December 30, 2023, 05:51:33 amIt is an indicator that current limiting circuit has been activated. This happens if the output is short circuited, or more usually, there is a fault in the device connected to the output.QuoteP2 = current limit control, adjustable between zero and max current.P1 = maximum current setting trimpotR5 = current sense resistorC5,C7 = feedback stability compensationQuoteWhen referenced to 0V the LM317 lowest adjustable voltage is 1.2V. If you require output voltage adjustment lower than 1.2V (for example 1V), then you need to go below 0V. P4 allows adjustment to exactly -1.2V

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 06:30:45 am
content: how to understand the resistor arrangement --P2,R3,R4,R6,P3.How the opamp is going to current Regulation?Thank you.

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 06:44:30 am
content: Quote from: ommsiva on December 30, 2023, 06:30:45 amP3 = voltage setting, not used for current regulationP2 = adjustable current limitIf LM301A pin 2 voltage < pin 3 voltage, then pin 6 goes positive, current limit disabled.If LM301A pin 2 voltage > pin 3 voltage, then pin 6 goes negative, which reduces the LM317 output voltage (and current).Pin 2 and 3 and the surrounding resistors are to measure the voltage across the current sense resistor R5. The more current through R5, the bigger the voltage.

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 08:13:59 am
content: Out of the two circuit, Which is best to built for application.

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 08:23:22 am
content: I definitely prefer the second one. Here's the original website:https://diodnik.com/laboratornyj-blok-pitaniya-svoimi-rukami-0-30v-0-5a/

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 08:41:08 am
content: Thank you sir.I need replacement for LM301 Ic , which i can use?Because LM301 has frequency compensation attached in the circuit.the main purpose of Frequency compensation is improvement in band width and at some frequencies negative feedback will be converted to positive feedback, to Avoid this. what is the relation with DC Regulated power supplies , how oscillation occur in RPS?

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 09:18:56 am
content: Quote from: ommsiva on December 30, 2023, 08:41:08 amThere is no direct replacement for LM301. It is possible to use different opamps, but they will require external frequency compensation, just minor circuit changes.QuoteThe oscillation in the power supply occurs during current limiting;1) When the current limit is active, it shuts down the LM317 so no more current.2) But no more current means the current limit will be deactivated, so the LM317 turns on and supplies more current again.3) But more current means the current limit is active again, it shuts down the LM317 so no more current..........and repeat the same cycle very fast, maybe around 500kHz, but the frequency depends on the output load.Compensation is intended to keep the loop frequency stable (too low frequency is bad, too high frequency is bad).If the compensation fails and the feedback changes from negative feedback to positive feedback, this can make the LM317 output maximum voltage, instead of the lower voltage. This may destroy your device connected to the output.

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 10:08:07 am
content: Here in this circuit , how BD139 acts as current limiter?Kindly Clarify this?

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 10:40:34 am
content: Quote from: ommsiva on December 30, 2023, 10:08:07 amThis circuit does not measure output load current, so it is not a current limiter in my opinion.It is possible the BD139 is screwed to the same heatsink as 2N3055, and it works as a temperature limiter (which also limits current).

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 10:46:56 am
content: I infer as a voltage reference before series pass element.

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 10:52:47 am
content: Quote from: ommsiva on December 30, 2023, 10:46:56 amAs the 2N3055 heatsink gets hotter, the BD139 (on the same heatsink) will change voltage, and turn off the 2N3055 which reduces the current. When it cools down, the BD139 turns on the 2N3055 again.The hot-cold-hot-cold-hot-cold is a feedback loop.

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 11:11:46 am
content: Hi ,from the below circuit , i understand that op1 is current limiter and op2 is voltage regulation opamp. I cant know the function of transistor and diode in the circuit. kindly help to understand the functionality

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 11:28:17 am
content: Quote from: ommsiva on December 30, 2023, 11:11:46 amWhich transistor?Which diode?Original design here:http://www.ok2cd.cz/reg.-zdroj-0---30v.html

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 11:39:28 am
content: The following components1)R1,C3,D1,D4,C4,R17,C15,D8,C14,LED2)T1,R3,LED2,R4,R5,C7,D6,R8,P1,R6,R7,C8,R9,D5,P23)C13,R13,T2,C10,C11,C12,D17WHAT WERE THE FUNCTIONS OF FOLLOWING COMPONENTS?

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 12:14:44 pm
content: Quote from: ommsiva on December 30, 2023, 11:39:28 amThese components form a -3.3V regulator for the opamp. The LED is separate, it is a power on indicator.QuoteThese components are for the current limit indicatorQuoteThese components are the current limiter. C7 is frequency compensation. P2 is the current limit adjustment control.QuoteThese components form a stable voltage reference.QuoteC13,C10 is frequency compensation. C11,C12 is output filtering. R13,T2 is the driver for BD139. Not sure what D7 is for.

author: ommsiva
author_rank: Regular Contributor
timestamp: December 30, 2023, 12:26:00 pm
content: Thank you..I am Confused , suggest a circuit which could can give regulated output (0-30V 0-10A).

author: Andy Chee
author_rank: Super Contributor
timestamp: December 30, 2023, 01:45:03 pm
content: Silicon Chip magazine had a variable 45V 8A a few years ago. Would this be suitable for you?https://www.siliconchip.com.au/Issue/2019/October/45V%2C+8A+Bench+Power+Supply+to+build(schematic only attached)

author: ommsiva
author_rank: Regular Contributor
timestamp: December 31, 2023, 02:18:52 pm
content: I require this specification(0-30V @ 0-10A) to charge the battery which are used in inverter. I request to suggest suitable power supply circuit for the specification. Thank you for the previous reply.

author: Andy Chee
author_rank: Super Contributor
timestamp: December 31, 2023, 02:31:55 pm
content: Quote from: ommsiva on December 31, 2023, 02:18:52 pmIt should be relatively easy to modify the previous circuit.If you examine the schematic and locate the pass transistors Q4, Q5, Q6, Q7 and their resistors. All you need to do is add one more transistor (and resistors). This will give you 10A.If you examine the schematic and locate the main transformer T1. Note that it has 2 x 40V windings. You can use a lower voltage 2 x 30V.

author: ommsiva
author_rank: Regular Contributor
timestamp: December 31, 2023, 02:41:34 pm
content: Thank you sir. How to analyse the given circuit? Because lot of passive device around IC makes the circuit more tough to understand.

author: Andy Chee
author_rank: Super Contributor
timestamp: December 31, 2023, 02:57:11 pm
content: The magazine article has an excellent analysis and description. I could not analyse better!You can purchase a copy of the October 2019 from their website:https://www.siliconchip.com.au/Issue/2019/October/45V%2C+8A+Bench+Power+Supply+to+build

author: ommsiva
author_rank: Regular Contributor
timestamp: January 02, 2024, 05:49:26 am
content: Hi,Went through the circuit, Cant understand how the circuit fixes output voltage..According to the condition , voltage divider near the output samples voltage across 10K and feed it to the ICa(inverting Amplifier) non inverting input. whether ICa is acting as a comparator or Inverting Amplifier?

author: Andy Chee
author_rank: Super Contributor
timestamp: January 02, 2024, 06:23:00 am
content: Quote from: ommsiva on January 02, 2024, 05:49:26 amYes you can treat IC1a as a comparator, which compares the voltage VSENSE to VSET.If VSENSE > VSET, then turn off LM317.If VSENSE < VSET, then turn on LM317.Again, this happens very fast, 500kHz or more. And in reality, it is not digital on-off, there will definitely be linear operation of the opamp.

author: ommsiva
author_rank: Regular Contributor
timestamp: January 02, 2024, 06:41:25 am
content: 1)That means it is fixed voltage regulator?(voltage across voltage divider at output) or how the voltage is variable?

author: Andy Chee
author_rank: Super Contributor
timestamp: January 02, 2024, 06:54:39 am
content: Quote from: ommsiva on January 02, 2024, 06:41:25 amVR3 is the voltage adjustment potentiometer.

author: ommsiva
author_rank: Regular Contributor
timestamp: January 02, 2024, 07:04:02 am
content: Suppose i want regulated output Voltage to be 10V. What are the following node voltage?1)Vsense2)vset3) Vout(ica)

author: Andy Chee
author_rank: Super Contributor
timestamp: January 02, 2024, 07:16:07 am
content: Quote from: ommsiva on January 02, 2024, 07:04:02 amVSET will be around 5.3VVSENSE will be oscillating between maybe 5.29 to 5.31, depending on load current.Pin1 of IC1a will also be between 5.29 to 5.31, but 180 degrees out of phase with VSENSE.

author: ommsiva
author_rank: Regular Contributor
timestamp: January 02, 2024, 07:28:22 am
content: Sir,"Pin1 of IC1a will also be between 5.29 to 5.31, but 180 degrees out of phase with VSENSE."ICa is acting as comparator, so output would be 29V(24-(-5) or 0V because output of opamp will be either +Vsat or -Vsat?. We are working with DC voltage, How phase reversal is possible? Kindly explain.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 02, 2024, 07:46:35 am
content: Quote from: ommsiva on January 02, 2024, 07:28:22 amAh! All feedback systems are AC, not DC.Even the LM317 regulator alone is an AC system, not DC.For example, have you seen inside the LM317? This requires small signal AC analysis, not DC!QuoteAs I alluded to before, there will definitely be linear operation between +Vsat and -Vsat. It is definitely NOT pure binary digital.

author: ommsiva
author_rank: Regular Contributor
timestamp: January 02, 2024, 07:54:44 am
content: 1)After rectification and Filtrations , the voltage become DC(Average voltage). So all the voltage present after filtering will be DC. Then how phase reversal is present?2) My doubt is , How output voltage is fixed? or How Voltage feed back is fixing output voltage?

author: Andy Chee
author_rank: Super Contributor
timestamp: January 02, 2024, 08:22:03 am
content: Quote from: ommsiva on January 02, 2024, 07:54:44 amThe 180 degree phase reversal is called negative feedback. I gave a binary explanation before:If x > y, then off.If x < y, then on.This is easy to understand, but does not reflect reality. In reality the negative feedback is continuous linear analog.REMEMBER: the output voltage of every regulator is not like a DC battery, it is never truly stable DC. It is always adjusting up and down i.e. AC. A good regulator has maybe 1mV AC. A bad regulator has maybe 200mV AC.

author: ommsiva
author_rank: Regular Contributor
timestamp: January 02, 2024, 10:39:00 am
content: 1) My doubt is , How output voltage is fixed? or How opamp feed back and adjustable regulator is fixing output voltage? probably give with a numeric example. Thank you sir

author: Andy Chee
author_rank: Super Contributor
timestamp: January 02, 2024, 11:48:59 am
content: If you're seeking numeric examples, the best way is to simulate it.Unfortunately I'm not good at simulation but there are others on this forum who are.I can show the basic circuit to simulate. The component types are incorrect, but you can replace them.

author: ommsiva
author_rank: Regular Contributor
timestamp: January 02, 2024, 05:07:15 pm
content: Sir, working on it. please find attachment.

author: ommsiva
author_rank: Regular Contributor
timestamp: January 07, 2024, 12:18:16 pm
content: Hi all,I have programmed the 317 IC with an output of 5V and Load suitably connected so that output current is 10 amps. I felt difficult to control current. Comment on the circuit, so that the circuit performance can be improved.Thank you all

author: ommsiva
author_rank: Regular Contributor
timestamp: January 07, 2024, 01:50:47 pm
content: Hi all,I went through this circuit , two current sense resistor(0.47 ohm) which is equivalent to 0.235ohm and current adjustable resistor 500 ohm were present in parallel.Can you explain how current limiting is working.

author: MarkT
author_rank: Frequent Contributor
timestamp: January 09, 2024, 10:05:30 am
content: D7 is ostensibly to protect the rest of the circuit if connected the wrong way to a battery perhaps? It will explode though, and fail in its task, unless its huge! I often charge batteries with my lab supply, but I know not to connect them reversed.Actually its probably really for the scenario where you totem-pole several bench supplies on top of each other for a range of voltages or for higher voltage.

author: ommsiva
author_rank: Regular Contributor
timestamp: January 16, 2024, 04:13:59 pm
content: QuoteP2 = current limit control, adjustable between zero and max current.P1 = maximum current setting trimpotR5 = current sense resistorC5,C7 = feedback stability compensationHow voltage accros R5 is sensed by P1,P2,R3 and How it is going to do the current Limitation?Kindly Explain...Thank you