Is there any way to control 40 V with a 5 V. I'm looking for some device to use the 5 volts like flipping a switch to allow the full 40 volts I've tried using all kinds of BJT and fet configurations, and I think I'm just hooking something up wrong. Thanks Colin
"Colin" schreef in bericht news:Xns969B7FF573D6Ctot@129.250.170.84...
Colin,
Guess some relay will do the trick. A P-channel MOSFET may do as well. It all depends on the current available from the control-voltage and the load you want to control with it. Also, it may be important to know whether or not the 5V and the 40V have a common (ground). Are they DC both?
petrus bitbyter
"petrus bitbyter" wrote in news:42e12cd6$0$779$ snipped-for-privacy@reader10.nntp.hccnet.nl:
The current from the control voltage is very low, something like .5 mA. I am trying to control a motor. Yes they are both DC, and no they don not have a common right now, but I think they can made common. Any help would be greatly appreciated, Thanks. Colin
"Colin" schreef in bericht news:Xns969B908D577DCtot@129.250.170.83...
-------------------------------+-------------40Vdc | |< + -| | |\ |< | +-------|TIP147| | |\ | .-. | | | | +----+ | |22k | o '-' | | | | .-. | 1N4007 - | |LOAD __ |/ ^ | | motor or relay 5V in -|___|--|BC546 | '-' 6k8 |> | | | | o ----------------+---------+----+--------------+---- | === GND created by Andy´s ASCII-Circuit v1.24.140803 Beta
Something like this.
The 0V or commons of both circuits should be connected to each other, called GND here.
When the 5V is on, the collectorvoltage of the BC546 should be below 1V. Otherwise you need to lower the 6k8.
The TIP147, drawn as two transistors, is one component called Darlington.
The TIP147 can be used for small motors only. Although it can handle up to
10A the inrush current of a motor can be much, much higher. Instead, you can use an appropriate relay as a load which in turn controls the motor.petrus bitbyter
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The circuit is great but the darlington transistor is a big power waster. The problem is that a darlington can't have a low Vce(sat), it will have at least 1 volt drop from emitter to collector. At several amps, that's several watts of power wasted and has to be dissipated with a heatsink. Use a PNP power transistor and a separate PNP driver transistor (see drawing above). The I limit resistor would be chosen to allow enough base current to fully saturate the power transistor at the maximum current.
Also it would be prudent to use a higher current diode across the motor. And another similar diode should be across the PNP power transistor, cathode to emitter, anode to collector.
You only need an NMOS and a diode. Gate to your 5 V control signal. Source to ground. Drain to the negative of your dc motor. Positive of your dc motor to 40 V. Also, connect the diode in parallel with the motor, but such that when the motor is on, the diode is reverse biased (i.e., cathode to 40 V, anode to drain). The NMOS must have a gate threshold voltage lower than 5 V, and a max Vds higher than 40 V. You didn't say how much current the motor needs. Depending on that, I can propose some specific NMOS and diode. The NMOS consumes only (and very little) during the state transitions, and nothing while in static conditions.
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