I tried to build a simple circuit that would send current through a resistor...

Dodgydave

Joined Jun 22, 2012
10,050
If you have a 5V regulator suppling the charger, why do you need to dump the voltage it will still be 5V, the only thing that will happen is the input to the regulator will rise??

What is the output voltage of the motor?
 

Thread Starter

eyik66

Joined Dec 15, 2012
30
You can add the PNP transistor to a TL431 programmable-Zener in the manner of a Szicklai pair.

You set the shunt voltage with a pair of resistors, make sure the added emitter follower PNP is enclosed in the nfb loop and the whole thing is as precise and sharp knee as the TL431.
I'll order a Tl431 and see if I can figure it out.
If you have a 5V regulator suppling the charger, why do you need to dump the voltage it will still be 5V, the only thing that will happen is the input to the regulator will rise??

What is the output voltage of the motor?
I suspect the voltage that is causing problems it the DC input to the regulator, after the rectifier. It must be exceeding the input limit on the regulator when the charger isn't pulling current.
 

ian field

Joined Oct 27, 2012
6,539
Everyone keeps asking that. A 7805 is rated for 24 V, but can withstand more.

ak
Years ago I fed a 555 via its own boost inductor and chopped Vcc with a MOSFET and flyback diode. When I checked what the Vcc was boosted to - it was around 30V. Various datasheets gave figures from 16 - 18V.

The particular part in question was of Hitachi manufacture, but I suspect a few other makes can get away with more ABS-MAX Vcc than the datasheet says.

Its just important to remember that the manufacturer only guarantees the part if you stay within the published spec.
 

AnalogKid

Joined Aug 1, 2013
9,354
The phrase I remember from an old National Semi seminar is that real opamps (+/-22 V rails) are made on a 60 V process line. Different seminar, TTL was made on a 12 V process line.

ak
 
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