Using 1N4001 Diode over 1N457 diode in a battery charging circuit - Page 1
Forum section: electronics / beginners

author: khatus
author_rank: Regular Contributor
timestamp: June 04, 2024, 06:58:57 pm
content: Hello guys, Can I use 1N4001 Diode instead of 1N457 Diode In this circuit?The 1N457 is a small signal diode.What is the purpose of this 1N457 diode here?

author: MrAl
author_rank: Super Contributor
timestamp: June 04, 2024, 07:50:04 pm
content: Quote from: khatus on June 04, 2024, 06:58:57 pmHello there,It's probably ok to use that diode as the diode function does not look very critical.A diode is sometimes used on the output of an op amp in order to make it look like an open collector so that it can not drive the other part of the circuit to some high level, only to a low level, allowing the rest of the circuit to assume the role of driving the output drive point high (the resistor). It could also be used to get a lower level output voltage for an op amp (such as this one) that can not get all the way to zero. Many op amps can not get all the way to zero, even sometimes with the rail to rail output op amps. A diode drops some of the output voltage allowing the cathode voltage to get a bit lower. In this case the diode does not ensure getting the output drive point voltage to zero, but it does lower it to a lower level than if it was not used.

author: MarkF
author_rank: Super Contributor
timestamp: June 04, 2024, 10:08:35 pm
content: You can use pretty much any jelly bean diode here. It is just part of the control logic.If you mask out the components that are not part of the control circuit it will be clearer.It's main function here is to pull-down R4 and place it in parallel with R1.The op-amp monitors the charging current via R6 and then adjusts the regulator outputwith the combination of R1 and R4.

author: wraper
author_rank: Unknown
timestamp: June 04, 2024, 10:17:48 pm
content: Should be fine, although 1N4148 would be more suitable choice.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 05, 2024, 08:17:51 am
content: The opamp is being used as a comparator and it's purpose is keep the base of Q1 from being driven high.It's low or nothing. Have a look at an LM393 for instance and see how its "open collector" output works.Note that most modern opamps won't work in this circuit, so be careful if substituting for the 301.The LED current limiting resistor is far to low for modern LED made after the 1970s.You dont need anywhere near that level of current. I'd up R5 to 3.3k or 4.7k to avoid blobs in your eyes.

author: David Hess
author_rank: Super Contributor
timestamp: June 05, 2024, 11:32:10 am
content: The 1N457 is a low leakage (non-gold doped) signal diode. A small signal transistor collector-base junction can replace the 1N457, but a 1N4001 or 1N4148 will work fine in this case. Any leakage will flow through R2+R3 to create an error in the output voltage.The diode allows switching between constant voltage and constant current mode. In constant current mode, the operational amplifier pulls the adjustment pin of the regulator low to control the output current. Once the current is low enough, the output of the operational amplifier swings high and the diode disconnects it from the adjustment pin so the regulator enters constant voltage mode.

author: MrAl
author_rank: Super Contributor
timestamp: June 06, 2024, 08:52:51 am
content: Hi,Yes good point, it behaves like a "wired OR" logic gate.Either the voltage can control the output 'OR' the current can control the output.This is typical in voltage control with kick in current control in circuits such as battery chargers and power supplies.