I'm designing a power supply for a small robot. I will use a 6V NiMH battery pack and I want to deliver 9V at 2A to drive the motors. I will use a step-up regulator to reach 9V but I don't know how to deliver 2A. Can anyone give me some hints about what should I study to project this circuit?
An easy way to identify potential parts that meet your requirement is to search for "boost regulator" on a site like DigiKey, then apply filters in the parametric search for the characteristics you require.
Also useful is some exploration of online tools for power management design, such as TI's Simple Switcher tools. Each manufacturer who offers such a tool, would propose parts and designs built around their respective product ranges, so it would behoove you to use several such tools to understand the types and prices of parts involved, before making a decision.
This exploratory exercise will also help gain some understanding of the simplest ways to implement a boost regulator for your project, if needed. Many of the free design tools go all the way through to providing reference schematics based on your inputs, plus costing for the bill-of-materials involved, and PCB area budget.
This isn't a direct answer to your question, but I think addresses the actual problem.
What you are doing sounds backwards. The motors are presumably by far the highest power devices in the robot. It therefore makes sense to tailor the battery back to them and convert the voltage as needed for the other purposes. In this case, arrange the battery pack to put out 9V or more. The step up regulator you propose will lose some power and will be fairly big. All this can be avoided by running the motors off the battery pack directly, then using much smaller buck regulators to power the lower voltage electronics.
Most likely you already have a motor controller in there that can effectively throttle back the motors as needed to attain the required position or speed. If that is the case, then the battery pack can be safely made to be a bit higher than the maximum effective voltage you are allowed to deliver to the motors. The controller will automatically lower the PWM duty cycle to compensate. For example, you might use a nominal 12V battery pack so that you still have the minimum 9V at the end of battery life. The buck regulators making 5V or 3.3V for the electronics will do that easily over a range of 9-12V.
NiMH comes in 1.2V cells, so if you must use 9V motors, then you ought to choose 8 cell batteries and factor aging effects on capacity when considering size.
Here is one source of 9.6V battery packs.
Words of advice.
- Note many are not recommended for motors.
- This has to do with the battery's ESR and current drain specs.
- Get the best you can afford for low ESR or max current rating.
- i.e. if your load is 2A then battery ought to be spec'd at 10A or more.
- Caution: Batteries cells must be extremely well matched to be packed in arrays. (<1%)