use bjt or mosfet in h-bridge with inductive load? - Page 1
Forum section: electronics / beginners

author: alireza7
author_rank: Regular Contributor
timestamp: July 25, 2018, 05:23:59 am
content: hiis it better to use 2 pnp bjt in high side and 2 npn bjt in low side of an inductive load drive h-bridge ?or using 2 pmos in high side and 2 nmos in low side of h-bridge?what are the advantages and disadvantages of using each one ?if our system is intended to drive a particular inductive load continuously for 10 years with switching frequency below 50Hz, which one seems to be more reliable and durable?

author: JS
author_rank: Frequent Contributor
timestamp: July 25, 2018, 05:43:19 am
content: What's the power level?Reliability depends a lot on the design, not only on the device. BJTs might seem more rugged as they don't have such a delicate part as the gate, but there are mosfet devices running for many years without problems, protect and drive propperly and you shouldn't have problems. Mosfets runs at loser temp, as a low rds on one will have way lower losses than a saturated. Bjt.JSJS

author: alireza7
author_rank: Regular Contributor
timestamp: July 25, 2018, 08:04:24 am
content: this is my schematic :i want to excite a (0.5H 200OHM) load with +- 20ma; with switching frequency below 50Hzfor protection i used two back to back 4.7v zener diodes connected to the load terminals as illustrated in my schematic .is this configuration of zener diodes a good way for protection? or i should use following configuration?

author: alireza7
author_rank: Regular Contributor
timestamp: July 25, 2018, 08:19:37 am
content: Quote from: blueskull on July 25, 2018, 05:52:57 amcan you please explain more ?i would be appreciated for any schematic .

author: alireza7
author_rank: Regular Contributor
timestamp: July 26, 2018, 08:17:41 am
content: Quote from: blueskull on July 25, 2018, 05:52:57 amin most bjt datasheets i just can find maximum rating of Collector −Emitter Voltage as a positive value and it seems that it's just corresponds to the positive voltages that one can apply to the Collector −Emitter.but what about negative Vce voltage which a bjt can tolerate?

author: alireza7
author_rank: Regular Contributor
timestamp: July 26, 2018, 08:38:17 am
content: Quote from: blueskull on July 26, 2018, 08:26:38 amso why bjt datasheets don't mention anything about this rating?

author: alireza7
author_rank: Regular Contributor
timestamp: July 26, 2018, 08:51:56 am
content: Quote from: blueskull on July 26, 2018, 08:45:53 amso as log as negative voltage that applies to the Vce is less than 6 volt i am in the soa and i don't need clamping diode?

author: alireza7
author_rank: Regular Contributor
timestamp: July 26, 2018, 09:06:06 am
content: Quote from: blueskull on July 26, 2018, 08:56:30 ami provide inductor current freewheeling path by using two back to back zener diodes.pleas look at my schematic :if l want to use inductor current freewheeling path by using 4 diodes like in following schematic , then the problem which i confront is that during switching time a negative current will go through +20ma current supply .

author: alireza7
author_rank: Regular Contributor
timestamp: July 26, 2018, 09:21:48 am
content: Quote from: blueskull on July 26, 2018, 09:10:25 ami think you mean add a 100uF on the output of the current source not the 5v rail regulator. am i right?

author: alireza7
author_rank: Regular Contributor
timestamp: July 26, 2018, 09:45:02 am
content: Quote from: blueskull on July 26, 2018, 09:33:27 amthanks i got it.my current source composed of a single nmos and a shunt resistors and op-amp like this:can i rely on nmos body diode and don't add any other extra diode?

author: David Hess
author_rank: Super Contributor
timestamp: July 27, 2018, 01:21:10 am
content: Quote from: alireza7 on July 26, 2018, 08:38:17 amThey do; it is Vbe.For power transistors, base-emitter breakdown is not as important as it mostly affects hfe at low currents.Using bipolar transistors or more likely Darlingtons even with external diodes may be less expensive than power MOSFETs simply because for a given current and voltage they use less silicon area making them less expensive. The advantage in speed that MOSFETs have does not matter at low frequencies.Bipolar h-bridges are also easier to drive because the same signal and driver may be used to turn on pairs of transistors.