I need to power a load with 1.5V or -1.5V MCU controlled. The circuit is powered with 1.5V so for getting the negative voltage I'm going to use a H-bridge.


simulate this circuit – Schematic created using CircuitLab

As said, the supply voltage for the load is 1.5V, or -1.5V, this will be controlled by the MCU (POS and NEG). Also the current input will be 200mA.

Which MOSFET will suit better this purpose?


Conections in the SPDT switch purposed by Andy aka:


simulate this circuit

  • \$\begingroup\$ What is your CPU IO voltage? \$\endgroup\$ – Andy aka May 8 '14 at 8:26
  • \$\begingroup\$ Knowing just what you've shown here, a Mosfet might be unnecessary. Does the load need to be able to switch direction very rapidly? If not, with these voltages and currents, power switching BJTs might be a better fit. How small should this be? \$\endgroup\$ – Sean Boddy May 8 '14 at 8:54
  • \$\begingroup\$ @Andy aka I still have to decide which MCU use between 2 or 3. What i can say is that the MCU will be powered with 5V, and the POS and NEG will be bit enabled, but I'm not sure of the voltage in the output pins \$\endgroup\$ – masmic May 8 '14 at 9:16
  • \$\begingroup\$ @Sean Boddy If I'm supplying the load with 1.5V and I want to change it to -1.5V, it must be considerably fast the change. \$\endgroup\$ – masmic May 8 '14 at 9:19
  • \$\begingroup\$ See Andy's answer. Unless you need to be able to switch very often, like thousands of times per second, then that analog switch IC should be fine. \$\endgroup\$ – Sean Boddy May 8 '14 at 9:23

At 200mA you are in the analogue switch range. What about the TS3A24159 from Texas: -

enter image description here

Your requirement is a little close to the max ratings but probably give enough clearance: -

On state switch current is +/- 300 mA and peak is + /- 500 mA

The point I'm making is that one little chip can do everything if you consider analogue switches - Vcc for the chip works down to 1.65V so your MCU should be above that and you feed the +1.5V supply through the switches to the load: -

COM1 and COM2 go to the load and you arrange NO and NC pins to form a H bridge: -


simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ I've had a look to it and I think it can suit my desing. Just I would ask you please to update your answer providing an example of how to do the conections to achieve the purpose of the eschematic I posted above, because i haven't got clear enought \$\endgroup\$ – masmic May 8 '14 at 9:44
  • \$\begingroup\$ @masmic_87 I've added a switch circuit that should help. SW1 and 2 operate together and are shown providing power+ to the top of the load resistor. When they switch power+ is applied to the bottom of the resistor. \$\endgroup\$ – Andy aka May 8 '14 at 10:29
  • \$\begingroup\$ Yes Andy thanks, I've adpated to my schematics and looks fine. Just one last doubt. I've updated the post with the resulting schematic for this switch, have a look if it is OK, and I have one last question. My MCU is powered with 5V and this switch with 1.5V. I suppose that in the IN pin where the MCU will provide the signal to select the voltage direction, the MCU output will provide more than 1.5V, and this would pass the switch's supply voltage, so, maybe I would need a swicht supporting 5V supply? or is it right this way? \$\endgroup\$ – masmic May 8 '14 at 11:00
  • \$\begingroup\$ The chip supply needs to be between 1.65 and 3.6 volts. I assumed a 3v3 MCU. \$\endgroup\$ – Andy aka May 8 '14 at 12:00
  • \$\begingroup\$ So, for a 5V MCU, i would need a version of this same chip that allows 5V supply, true? \$\endgroup\$ – masmic May 8 '14 at 12:37

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